1. Field of the Invention
This invention relates to a method of detecting an edge of a tape with a magnetic head device, and to a method of detecting a tape edge applicable to a tape recorder used with a computer for storing back-up data.
2. Prior Art
In a tape recorder using a magnetic tape as a recording medium, a head gap is required to accurately trace a predetermined recording track. The recording track on the magnetic tape is determined or set, using the edge of the magnetic tape as a reference. Therefore, in order that the head gap can accurately trace the predetermined recording track, it is necessary to detect the tape edge beforehand. For example, particularly when a magnetic tape is used in a tape recorder used in a computer for storing back-up data, the magnetic tape is divided into many recording tracks, and therefore it is important to detect the tape edge beforehand.
In one known method of detecting a tape edge, a magnetic head device for recording and reproducing signals is utilized for such tape edge detection. One example of such method is disclosed in U.S. Pat. No. 4,476,503. In this conventional method of the U. S. patent, as shown in FIG. 13, there is employed a magnetic head 11 capable of reading after writing and having a write gap Wg and a read gap Rg which are arranged in juxtaposed relation in the direction of travel of a tape 4. A screw 17 is threaded into the magnetic head 11, and is adapted to be rotated by a stepping motor 15, so that the magnetic head 11 can be moved in the direction of the width of the tape 4. When the tape 4 travels or runs from the left to the right in FIG. 13, a signal is recorded on the tape 4 by the write gap Wg, and also the recorded signal is read by the read gap Rg. In this manner, the signal is recorded and read, and at this time the magnetic head 11 is moved in the direction of the width of the tape 4. When the center of the read gap Rg registers with the edge 4a of the tape 4, the output level of the signal read by the read gap Rg becomes 1/2. Therefore, the position where the output level of the signal read by the read gap Rg becomes 1/2 is detected, and this position is determined as the tape edge position.
In the tape edge detection method described in the above-mentioned U. S. patent, the signal written by the write gap Wg is read by the read gap Rg. When the output level of the thus read signal reaches the predetermined level, this position is determined or set as the tape edge position. Therefore, the tape edge is detected by the center of the read gap Rg.
In the case where a single magnetic head is provided with a write gap and a read gap, the center of the write gap is often out of alignment with the center of the read gap in the direction of travel of the tape. This results in a problem that the signal written by the write gap is detected by the read gap displaced or offset relative to the write gap, thereby causing an error in the result of the tape edge detection. Another problem is that an azimuth deviation developing when mounting the magnetic head on a tape drive device also leads to an error in the result of the tape edge detection.